1. Field of the Invention
The invention relates to a process for treating nonferrous metal hydroxide sludge waste containing chromium, copper, zinc, and nickel as nonferrous metals and recovering the nonferrous metals by separating the individual nonferrous metals from one another.
2. Description of the Prior Art
Hydroxide sludge waste obtained from galvanic processes or in the nonferrous metal processing industry generally contains the following components (data in weight %):
______________________________________ Water 40 to 90, on the average 70 Iron 0 to 10, on the average 2 Aluminum 0 to 2, on the average 0.5 Chromium(III) 0 to 10, on the average 2 Zinc 0 to 10, on the average 2 Copper 0 to 5, on the average 1 Nickel 0 to 5, on the average 1 Calcium 0 to 20, on the average 4 Sodium 0 to 2, on the average 0.5 Silicic acid 0 to 5, on the average 1 Cyanide (complex) 0 to 0.1 -- -- Sulfite + -- -- Carbonate 0 to 5 -- -- Chloride + -- -- Sulfate -- -- ______________________________________
This hydroxide sludge waste has too high a water content and too low a concentration of valuable metals to allow an economic smelting process to be carried out. As a waste material, however, it contaminates the environment and must be disposed of only on special garbage dumps, which is very expensive. For this reason, clean removal or destruction of the waste is necessary. However, working up of the waste with recovery of the contents is highly desirable.
It has already been proposed that such waste be disposed of by admixing it in the manufacture of bricks. Furthermore, process methods are known from hydrometallurgy and from wastewater treatment, which permit the recovery of one or two components, although even those processes have proven unsatisfactory. None of the processes allows the recovery of several of the components satisfactorily.
Moreover, there are numerous processes for separating out metals in fixed-bed ion exchangers or for removing them from effluent waste solutions. By means of these processes, a selective separation of valuable nonferrous metals is not achieved. Generally, mixed solutions are obtained, which are precipitated together and the resulting residue must then be disposed of as waste sludge.
A process for the recovery of copper and zinc from nonferrous metal scrap is disclosed in German Offenlegungsschrift No. 23 40 399. According to this process, the sludge is leached with an ammonium carbonate solution in the presence of oxygen. Subsequently, the metals are separated from the leaching solutions containing copper ammonium carbonate or zinc ammonium carbonate. Such a process cannot be used for working up nonferrous metal hydroxide sludge waste, since the calcium content inferferes with the ammonium carbonate equilibrium and since, in addition, the chromium hydroxide would remain in the residue.
The recovery of copper and nickel by liquid-liquid extraction from ammoniacal solutions is known, as is the liquid-liquid extraction of copper at pH values of 1 to 3. These processes work in conjunction with an electrolysis treatment whose terminal electrolyte is used for stripping the metal-laden organic phase. Furthermore, there are processes for extracting zinc with organic liquids from zinc-containing sulfuric acid solutions and stripping this zinc with the terminal electrolytes of an electrolysis. It is common to all of these extraction processes described that the separation can only be carried out in the absence of iron, calcium, aluminum and chromium impurities.
Attempts to selectively precipitate the nonferrous metal compounds from the waste sludge have failed because of the co-precipitation of considerable amounts of impurities.